1. Field of the Invention
This invention relates to a variable reluctance type angle detector having a rotor having such a shape that a gap permeance varies in a sine wave fashion with respect to an angle θ, the rotor being provided rotatably on a stator having teeth on which an excitation wire and an output wire are wound.
2. Description of the Related Art
As a conventional variable reluctance type angle detector, one having a rotor rotatably provided at the center of a stator having an excitation wire and two-phase output wires are wound has been known. A stator core has twelve teeth disposed on a circumference and projecting inward.
The excitation wire is wound around the teeth in such a fashion that polarities of the adjacent teeth are different from each other to form excitation coils. The two-phase wires are wound around the teeth so as to achieve a SIN output and a COS output whose phases are different from each other by 90 degrees, thereby forming output coils. The rotor has such an outer shape that the gap permeance varies in a sine wave fashion with respect to an angle θ. When the rotor is rotated, an excitation voltage supplied to the excitation wire is outputted from one of the output wires as a COS output voltage, while a SIN voltage is outputted from the other output wire. Such variable reluctance type angle detector is disclosed in JP-A-8-178611.
FIG. 4 is a diagram schematically showing a wire structure of the excitation wire and the two-phase output wires wound around the twelve teeth. In FIG. 4, the teeth are denoted by numbers 1 to 12 sequentially along a circumferential direction for the convenience illustration. The excitation wire is wound around each of the odd number teeth while being negatively wound around each of the even number teeth. The numbers of windings of the positive winding and the negative winding are identical to each other.
As shown in FIG. 4, the output wire outputting the COS output voltage is wound positively and negatively in an alternate fashion along the circumferential direction. The numbers of the positive windings and the negative windings of this output wire are varied tooth by tooth in order to achieve the COS output. The output wire outputting the SIN output voltage is wound positively and negatively in an alternate fashion along the circumferential direction. The numbers of the positive windings and the negative windings of this output wire are varied tooth by tooth in order to achieve the SIN output.
In the conventional variable reluctance type angle detector, the three layers of the excitation wire and the two-phase output wires are wound around one tooth. Therefore, it is necessary to secure insulation at two interlayer parts in each of the teeth. In the conventional variable reluctance type angle detector, an insulating layer is not ordinarily used for the insulation of the interlayer parts, while an enamel layer formed on surfaces of the excitation wire and the two phase output wires secures the insulation. However, when the parts to be insulated are increased in number, probability of insulation failure due to stripping of the enamel layer or the like is increased.
In order to increase the output of the conventional variable reluctance type angle detector, the numbers of windings of the two-phase output wires are increased. Since the three layers of the excitation wire and the two-phase output wires are wound around one tooth, it is necessary to increase a capacity of a slot for the purpose of increasing the winding number. As a result, a problem of increase in size of the variable reluctance type angle detector occurs. Also, when the numbers of windings of each of the excitation wire and the two phase wires are increased in each of the teeth, the time required for winding work is increased, thereby undesirably causing an increase in cost.